1. Field of the Invention
The present invention relates to the intravascular-ultrasound (IVUS) arts, or more particularly, to a system and method of using ultrasound data backscattered from vascular tissue to estimate the transfer function of a catheter (including components attached thereto—e.g., IVUS console, transducer, etc.).
2. Description of Related Art
Ultrasound imaging of the coronary vessels of a patient can provide physicians with valuable information. For example, such an image may show the extent of a stenosis in a patient, reveal progression of disease, determine the vulnerability of the atherosclerotic plaque for causing myocardial infarction, help determine whether procedures such as angioplasty or atherectomy are indicated, or whether more invasive procedures are warranted.
In a typical ultrasound imaging system, a catheter (including an ultrasonic transducer attached thereto) is carefully maneuvered through a patient's blood vessel to a point of interest. Acoustic signals are then transmitted and echoes (or backscatter) of the acoustic signals are received. The backscattered ultrasound data (“backscattered data”) can be used to identify the type or density of the tissue being scanned. When the echoes (or multiple sets thereof) are received, acoustic lines are processed, building up a sector-shaped image of the blood vessel. After the backscattered data is collected, an image of the blood vessel (i.e., an intravascular-ultrasound (IVUS) image) is reconstructed using well-known techniques. This image is then visually analyzed by a cardiologist to assess the vessel components and plaque content.
One drawback of such a system, however, is that the ultrasound data backscattered from the vascular tissue may not accurately represent the tissue. This is because the backscattered data may further include a noise component and a catheter component. For example, with respect to the latter, manufacturing tolerances can cause different catheters (or devices connected thereto—e.g., IVUS console, transducer, etc.) to operate differently (e.g., at slightly different frequencies, etc.), thus producing different results. This influence on the system is referred to herein as the “transfer function.”
Traditionally, the transfer function has been determined (i) with the catheter outside the patient and (ii) through the use of a perfect reflector (e.g., plexiglass, etc.). Specifically, the catheter would be positioned near the reflector and used to transmit ultrasound data toward the reflector and to receive ultrasound data backscattered from the reflector. Because the reflector backscatters all (or substantially all) of the data transmitted, the catheter's transfer function can then be computed. This is because the backscattered data (B) is equal to the transmitted data (T) as modified by the transfer function (H) (i.e., B=TH). Drawbacks of such a system, however, are that the transfer function cannot be computed in real-time (e.g., while data backscattered from vascular tissue is being acquired, etc.) and requires the use of additional components (e.g., a perfect reflector, etc.). Thus, it would be advantageous to have a system and method for determining the transfer function of a catheter that overcomes at least one of these drawbacks.